// for...in 标准化: ECMA
const obj = {
  name: "why",
  age: 18,
};

for (const item in obj) {
  console.log(item);
}

const arr = [1, 2, 3, 4];
for (const item of arr) {
  console.log(item);
}
for (const item in arr) {
  console.log(item);
}
